A thermal processing chamber as used herein refers to a device that rapidly heats objects, such as semiconductor wafers. Such devices typically include a substrate holder for holding a semiconductor wafer and a thermal energy source, such as a light source that emits energy for heating the wafer. During heat treatment, the semiconductor wafers are heated under controlled conditions according to a preset temperature regime. For monitoring the temperature of the semiconductor wafer during heat treatment, thermal processing chambers also typically include temperature sensing devices, such as pyrometers, that sense the radiation being emitted by the semiconductor wafer at a selected band of wavelengths. By sensing the thermal radiation being emitted by the wafer, the temperature of the wafer can be calculated with reasonable accuracy.
Many semiconductor heating processes require a wafer to be heated to high temperatures so that various chemical and physical reactions can take place as the wafer is fabricated into a device. During rapid thermal processing, which is one type of processing, semiconductor wafers are typically heated by arrays of light sources to temperatures, for instance, from about 400° C. to about 1,200° C., for times which are typically less than a few minutes.
For instance, in the past, semiconductor wafers were heated according to a predetermined heating cycle. For example, the wafers were typically heated from an initial temperature to a desired temperature at a very fast heating rate. The wafers were then maintained at the desired temperature for a time sufficient for desired processes to take place. For instance, during these heating cycles the wafers can be annealed or various coatings and films can be deposited onto the wafers, such as oxide films. In order to complete the heating cycle, the light sources are switched off and the wafers were allowed to cool after being maintained at a desired, temperature for a predetermined amount of time. In general, the wafers were allowed to cool by simply removing or turning off the heating source. Moreover, in some cases, a cooling device was also used to cool the wafer.
Recently, emphasis has been placed upon forming integrated circuits having thinner and more uniform layers that are more efficient and require less power to operate. In this regard, recent focus has turned to not only more precisely forming coatings and films in thermal processing chambers, but also on reducing the length of time it takes to complete a heating cycle in the chamber, e.g., temperature ramp-up, a steady state temperature, and cooling. In general, to accomplish the desired results, the wafers must generally be heated and cooled as uniformly as possible.
However, one problem with heating and cooling semiconductor wafers is that the temperature profile of a wafer can vary at different wafer locations, thereby decreasing overall heating and cooling uniformity. For example, when forming an oxide layer on a silicon wafer using conventional processing systems, the temperature profile of the wafer typically has deviations from the desired uniform temperature that are due to a variety of factors, such as the type of heaters utilized, geometry of the chamber, etc. These deviations are typically localized in only certain regions of the wafer. For instance, localized temperature deviations can be prevalent during the ramp-down and ramp-up stages of the heat cycle. During such stages, the localized outer regions of the wafer tend to heat or cool faster than the localized center region. This leads to non-uniformities in temperature profile across the wafer.
Such localized temperature deviations typically have a magnitude on the order of a few degrees and are localized in regions of centimeters on the wafer. In particular, in rapid thermal processes, the deviations are usually in the range from about 0.1% to about 10% from the target uniform temperature. For example, a typical localized deviation in a conventional rapid thermal processing system is about 5° C. for a target process temperature of about 1,000° C.
As such, a need currently exists for an improved apparatus and process for cooling and heating wafers in rapid thermal processing chambers. In particular, a need currently exists for a rapid thermal processing chamber that is capable of locally cooling and/or heating a semiconductor to minimize deviations in the temperature profile of the wafer.